Same here, X and I'm still in game. The dude (well I think it was a dude xD) said he needed to leave and by accident I X'ed instead of ending via the ending options. Now I've been in the game for more then 10 minutes after I left xD Kinda annoys me to, because it also prevents me from playing my self, not to mention others who also can't play. I'm pretty sure you can make a pop up appear that says you need to end the game properly, or just make it so it automatically ends when you X.
On the topic of online dueling, I sometimes think it moves too fast. My opponent can make moves faster then I can type and then I have to ask to reverse or we need to agree on something else. Something very simple though to resolve that is to just leave pauses, let your opponent do damage calc when you attack and stuff like that. I'm also thinking about making a small program that can type preset texts, like all the phases, if you want to activate an effect or even if you want to chain. Just so I don't have to type the same things a thousand times during a single duel ^^
I've also noticed a lot of people don't know that you can click a card to view all it's data, and that very few people know the Genex monsters ^^

you can just click on the card? I didnt know that, something I usually do is if there deck is public I click one it so that when they use specific cards i can make sure they aren't cheating, but now I can just click on the card thanks for tellin me!